Spider silk, which has been evolving for over 450 million years, has a tensile strength greater than steel and elasticity greater than nylon. A number of spider silk genes have been cloned and sequenced revealing specific amino acid motifs that have been conserved for over 125 million years. The key element in taking the next step toward generating bio-based materials from spider silks will be to move from the current descriptive data to predictive knowledge. These experiments will provide the predictive knowledge enabling the design of materials with very specific elastic and strength properties for each different medical application. This renewal is designed to continue testing two basic hypotheses and engineering concepts. 1) The elasticity of the materials will be proportional to the number of elastic motifs. 2) Varying the sequence of the elastic regions will vary elastic (Young's) modulus. A brief workplan is described here. 1) Continue the expression and purification of the proteins. 2) Optimize the spinning and film making process to maximize desired materials properties. 3) Test mechanical properties of films and fibers. 4) Determine the structure of the protein in films and fibers by FTIR, CD and solid state NMR. 5) The elasticity and tensile strength data will be correlated with the number and sequence of each type of motif to produce a prediction algorithm for elastic and tensile strength properties. 6) Based on 5) new genes will be constructed to match the properties needed for ligament and tendons. The past two years of work have produced a number of new genes, purified proteins and fibers from those proteins. Improvements in fiber spinning and testing of those fibers is currently in progress. This project is highly significant for several reasons. First it will provide a basic understanding of elasticity and tensile strength in spider silk proteins. Specifically, it will reveal what controls the amount of elasticity and elastic modulus and if these two factors can be varied in a predictable way. Second this project will advance our ability to use spider silk as a biomaterial. If our hypotheses are correct we will learn how to control the elasticity and other materials properties by controlling the protein sequence. Possible applications of spider silk range from artificial ligaments and tendons to bandages for burns to composite materials for multiple applications.